A packaging paper for food has to fulfill many different and partially contradicting requirements. A first function of the packaging paper is to protect the packaged food from environmental influences. This requires at least a certain mechanical strength and a chemical stability against typical environmental influences. A second function consists in that the packaging paper should also protect the environment from influences by the packaged food, with which it might come into contact. Above all, for food this requires a sufficient resistance against the penetration of grease, oil and water through the packaging paper. Additionally, the packaging paper for food should have a defined resistance against the penetration of water vapor, on the one hand to prevent the food from drying out too quickly and on the other hand, particularly for warm food, to prevent water vapor from condensing inside the packaging and moistening the food.
A further important property is a good printability of the packaging paper, at least on one side, as many packaging papers for food are printed, in order to be able to identify the packaged food and its origin and in order to provide an attractive appearance to the packaged food. This can be done, for example, by flexographic printing, offset printing or roto-gravure printing. It is also important that the packaging paper does not stick to the packaged food and in addition, the packaging paper should lie flat and have pleasant haptics, a high opacity and a good foldability.
As packaging paper for food is often used only once, it is sensible for ecological reasons that the packaging paper can be recycled as easily as possible, or if it is not disposed of properly that at least it can be degraded biologically.
Typically, the requirements of a high or defined resistance against the penetration of grease, oil, water and water vapor and good recyclability or biodegradability contradict each other.
A process known from the prior art for packaging papers to achieve a good resistance against the penetration of grease, oil and water or water vapor, respectively, consists of coating a base paper on one side with polyethylene, for example, in an extrusion process. Because of this coating, such a paper cannot be recycled as waste paper or it can only be recycled with a great deal of effort. Thus, this process does not entirely satisfy the requirement of recyclability or biodegradability.
Another process known from the prior art for packaging papers in order to achieve a very good resistance against the penetration of grease, oil and water consists of coating the paper with specific fluorine-containing substances. In particular polyfluorinated surfactants, and above all fluorotelomer alcohols, CF3(CF2)CH2CH2OH with n being uneven, have been proved to be suitable for this application. The use of these substances, however, can cause a contamination with perfluorooctanoic acid (PFOA, C8HF15O2), which accumulates in the human organism and is classified in the REACH (Registration, Evaluation, Authorisation of Chemicals) regulation in force in the EU as a reproductive toxicant, carcinogenic and toxic. For this reason alone, polyfluorinated surfactants are not desirable as a component of a packaging paper and in particular not as component of a packaging paper for food. Additionally, such papers are almost incapable of being recycled.
Many attempts to coat a packaging paper for food with substances of primarily biological origin, so that in addition to good recyclability or biodegradability, a high resistance against the penetration of grease, oil and water could also be achieved, were not successful, because the high resistance against the penetration of grease, oil and water, which coatings with poly-ethylene or the use of polyfluorinated surfactants offer, could not be even approximately obtained.
In other attempts to coat the packaging paper with petroleum-based waxes, a high resistance against the penetration of grease, oil and water could be achieved, but again, the requirement for good recyclability or biodegradability was not fulfilled to a sufficient extent. Furthermore, these waxes are often based on petroleum products and are for this reason alone ecologically disadvantageous.
Therefore, there is still a great need in the industry for an even better combination of these two essential requirements for a packaging paper for food.